1. Field of the Invention
This invention relates to rubber compositions suitable particularly for use in automotive tire treads.
2. Description of the Prior Art
Industrial attention is directed to resource and energy saving. To cope with this trend, automobile tire manufacturers have made research efforts to develop high-quality, fuel-saving tires.
Carbon black is well known as an important filler to reinforce rubbers. Its physical characteristics are determinable by the specific surface area on I.sub.2 or BET adsorption and also by the carbon structure on DBP adsorption.
Improved abrasion resistance and reduced heat buildup are essentially required of carbon black-filled rubber compositions for use in tire treads. The filler if larger in surface area or if denser in carbon structure would render the resulting tire highly immune to heat development but less resistant to abrasive wear.
In general, automobile tires are susceptible to hysteresis loss mostly at their tread portions. Certain hysteresis-resistant rubbers have been proposed to compensate for this problem, and they include natural rubber, synthetic isoprene rubber, butadiene rubber and low glass transition styrene-butadiene rubber and their blends. Common additives are carbon black of a relatively coarse particle size and softeners of an aromatic oily type but in limited quantities. The prior hysteresis-resistant rubbers, though economical of fuel, are satisfactory from the functional point of view. Too coarse carbon black would fail to give improved resistance to wet skid and to abrasive wear. Less softeners would invite excessive rigidity, hence serious skin on snowy and icy roads.
With both fuel economy and skid resistance in view, other types of butadiene rubber and styrene-butadiene rubber have also been proposed which have a 1,2-vinyl bonds content greater than 50%. Such vinyl-rich rubbers, however, undergo glass transition at relatively high temperatures and thus would make the tire severely abrasive and too rigid and skiddy on snow and ice. This leaves the problem that the driver will have to replace his car tires with spiked or studded tires, which is literally tedious and time-consuming.